Galvanometer



L. OBRYAN GALYANOMETER Aug. 22, 1944.

Filed July l5, 1943 www nlllllllllllll llllllllllllllllllll l I Qq. H a 4 4 K Inventor: Lovin OBryan, by wwwq Hs Attohn ey Patented Aug. 22, 1944 (SALVANOMETERV Lorin OBryan, Scotia, N. Y., assigner to General Electric Company, a corporation of New York Application July 15, 194s, serial 15.494.775 s claims. (c1. 17195 My invention relates to galvanometers and in particular to improvements in the4 form of galvanometer described in United States Patent No. 2,326,252, August 10, 1943, of Theodore A. Rich and assigned to the same assignee as the present invention. In the Rich patent there is described a flux meter with a suspension type moving coil andv a stationary permanent magnet eld with auxiliary permanent magnet means to compensate for the torque of the suspension and minimize drift. The primary object of my invention is to simplify the construction and improve the action of the auxiliary compensating means and also to provide for an adjustment for the same by:

means of which the drift tendency in opposite dipresence, in the vicinity of the instrument, of disturbing magnetic influences.

The features of my invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. For a better understanding of my invention,.reference is madeinl the following description to the accompanying drawing in which Fig. 1 represents a partially sectioned front view of a suspension galvanometer embodying my invention; Fig. 2 a partially sectioned side view of the same galvanometer; Fig. 3 a top sectional view taken on line 3- 3, Fig. 1; and Fig. 4 is a' perspective view of certain parts of the galvanometer illustrating the iflux paths involved in the operation and adjustment of my invention.

The main magnetic elements of the galvanome ter concerned with my invention may be seen in Fig. 4 and comprise 'a current conducting coil I2 which, when the instrument is used as a ilux meter, may be connected in series with a search coil located in the flu'x field to be measured.- Permanent magnet eld producing means are provided for cooperating with the current conducting Acoil I2 having pole pieces I4 and I5. Sixteen (I6) torqueV of the torsional suspension comprising wires 22 and 23. Spaced from and in ux shunting relation with respect to the compensating magnet I6, are soft iron shu-nting elements I'I Y and I8, which elements are adjustable towards and away from magnet I6. These compensating parts are located in the path of leakage flu-x from the main-permanent magnet fleldvof the instrument as represented by dotted lines. Also located p in such leakage flux field is a soft iron element I9 which is adjustable about the axis of the suspension so as to adjust the division of the leakage rections can be equalized when upset due to the represents a tiny permanent magnetsecured to i the moving system for compensating for the ilux between parts Il and I8. The suspension carries a mirrorr20 for deflection indicating purposes. As will be described in connection with Figs. 1, 2, and 3, the galvanometercomprises an outer magnetunit and supporting closure 9 and an inner re- `movable unit I0 which carries the suspension. l

The galvanometer is of rugged construction but has high sensitivity.A .The innerA unit is removed from the outer unit by withdrawing the inner unit downward from the bottom.

' The removable unit I0 consists of the moving system, a magnetic `core 3l, and their support (see Figs. 1, 2, and' 3) The coil I2, in the form of galvanometer illustrated, is suspended within the removable unit IIJ or supporting member by means of a marine type o f torsion suspension consisting of wires 22 and 23, each secured at one end to the coil I2v and connected electrically and mechanically at the other end to a resilient mounting such as a leaf spring 24. The main supporting structure consistsofa'pair of longitudinal strips 2I having the shape off segments of a hollow cylinder and composed of insulating material such as phenolic condensation product. The removable unit I0 includes also circular vcup-like members 25 and 26, at least one of which, for example, the latter, is rotatably mounted within the removable unit IIJ. The springs 24 are secured and electrically connected to the members'25 and 26. In the arrangement 'illustrated' the strips 2I are secured to the member 25y at the upper ends and are secured atA the lower ends to a ring 26', within which the member 26 is supported with freedom to be rotated. Any suitable suspension may be employed. I have obtained satisfactory results by ,the employment of a rectangular cross-section 14-karat gold wire, which is rolled from a wire one and one-half mils in diameter, has a breaking strength of grams, and provides a torsion of 1.2 dynecentimeters per centimeter. Since the movable armature or coil "I2 weighs only 1.2 grams, the apparatus has a high factor of safety with great ability to withstand shock. The gold suspension wires 22 and 23 are electrically connected t0 the coil AI2 to serve also as lead-in wires.

be completed; a contact strip 21, composed of a suitable metal such as copperor brass, is securedl V In order that an electrical' circuit to the rotatable coil may I4 and I5.

Fig. 3 to receive the contact strips 21 and 29. Contact springs 3| and .32, electrically connected to terminal studs 33, are provided in the outer galvanometer unit 9 and are so arranged that the contact strips 21 and 29 will make contact with the springs 3| and 32 when lthe removable member I6 is mounted in place as shown in the drawing.

Secured to the lower end of the current conducting coil I2 is a light rod of suitable composition, such as aluminum tubing 34, andthe torque compensating magnet I6 is carried'at the lower end of the rod 34 in order to remove the magnet I6 from the immediate influence of the principal magnetic field of the galvanometer. In the case of a galvanometer with thepreviously described one and one-half mil suspension, the high coercive force permanent magnet I6 need be only .075 in. by .006 in. by .020 in. A suitable composition for the magnet I6 is 24 per cent cobalt, 8 percent aluminum, about 3 per cent copper, 13 per cent nickel, and the balance iron magnetized hot and aged after hot magnetization for about four hours at a somewhat lower temperature without magnetic eld. However, other high coercive force materials may be employed. Secured to the current conducting coil I2 is also a suitable deflection indicating device, in this case shown as the light reflecting mirror 20 carried at the upper end of a light brass strip 36, which is secured to the upper end of the current conducting coil I2. To increase the sensitivity ofthe galvanometer by minimizing the magnetic reluctance of the magnetic circuit, a soft iron core 31 is secured to the longitudinal strips 2I within the coil I2. IStops for preventing excessive deiiection of the coil I2 may also be provided if desired. If desired, a cap 39, serving as a zero adjusting knob, may also be secured to the lower cuplike member 26.

For` providing a unidirectional magnetic eld cooperating with the deecting current conducting coil I2, permanent magnet means are provided consisting of a pair of bar magnets 46 and 4I making magnetic contact with the pole pieces Together, with suitable supporting and enclosing members, the bar magnets and pole pieces form the outer galvanometer unit 9, which serves as an external housing and support for the galvanometer. The outer unit 9 includes a flanged supportingmember 42, an upper enclosing shell 43, vand a lower enclosing shell 44.

- The shells are composed of a suitable insulating material such as synthetic plastic. The upper shell 43 carries the terminals 33 and the contact strips 3I` and 32 which are made stiff enough to hold the removable unit I within the outer unit by frictional engagement. The flanged member 42 is adapted to be bolted to`supporting brackets (not shown). `It may be composed of nonmagnetic material and fastens together the magnets 40 and 4I and the pole pieces I4 and I5, and may be made integral with the lower sleeve 44. Preferably the parts 43and '42 have recessed surfaces into which the magnets and pole pieces t, Y

and the parts are held together by machine screws in the pole pieces as shown in Fig. 2. The magnetic flux shifter I9 is carried in an internal recess in a collar 45 of insulating material which has a bearing t about the shell part 44. lA deformed washer-shaped spring 46 is inserted between theV collar 45 and the underside of ange 42, and the collar is urged upward against mild spring tension by pins 41 beneath the collar and preferably in recessed lower surface parts of such collar, so that the collar may beturned on sleeve I. parts I1 and I8, as represented in Fig. 1, and

may be shifted by rotating collar 45 so as to divide this leakage ux between shunting parts I1 and I8-in any desired relation.

The magnetic shunts I1 and I8 are carried on non-magnetic flexible arms 48 and 49, the upper ends of whichnare held by being inserted in grooves in opposite sides of `the core part 31 and clamped therein by the strips 2| (see Fig. 3J. The shunting pieces I1 and I8 may be adjusted towards and away from the tiny permanent magnet I6 by screws 50 which extend through and arex carriedby the strips 2I. This assembly is completely carried by the inner removable member VI 0, butthe screw heads are accessible through openings 5I in the outer housing shell 44, so that the positions of the shunts I1 and I8 are adjustable when the galvanometerA is completely assembled as'well as-before assembly of the inner and outer parts 9 and I0. To prevent accidental adjustment of parts I1 and I8 against the suspension 23 the lower ends of springs 48 and 48 act as stops against the upper end of sleeve 26. The tiny permanent magnet I6 is positioned close to but not touching the suspension 23 between the shunt pieces I1 and I8 by a light aluminum tion end for end and thus produces torques opposite to and proportional to the torsional torques of the suspensionwhen the coil I2 is` deflected from zero or central position within the rame of the deflection which is not over 45 degrees Aeither way from center position. Thel shunting pieces I1 and I8 divert or shunt apor` tion of the leakage iiux from the permanent magnet I6 and since these shunts are adjustable towards and away from the permanent magnet,

I6, `the counter-torque produced by the latter may be nicely adjusted to be equal to the sus' pension torque in both directions from neutral position with the result that the drift of the suspended coil is negligible. Following a flux measurement and corresponding deection of mirror 20, the deilection is retained for a suffi- Y cient length of time as to enable readings to be taken leisurely and accurately.

When the galvanometer is mounted in place and the shunts I1 and I 8 properly adjusted so that there is minimum drift, it may so happen Vthat due to the presence of other magnetic material or stray elds in the vicinity, the delicate magnetic adjustment for drift is disturbed. ThisY X and other disturbing magnetic iniiuences of like nature, the position of iiux shifter I9 may be altered. In this case, I9 would be shifted to the asaeos right more in line with shunt piece IB, thereby shifting some stray flux from shunt I1 to shunt I8 and producing a uniform stray field in the vicinity of magnet I6. The final adjustment may require a readjustment of shunt pieces I1 and I8 also. I have found that by means of the adjustments described the countertorque of the suspension may be compensated for and thc compensation made equal for either direction of deflection of the suspension from neutral, notwithstanding the presence or absence of other mild disturbing magnetic influences likely to be encountered in practice.

In accordance `with the provisions of the patent statutes, I have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried y out bv other means.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A galva-nometer comprising stationary permanent magnet means for producing a' ux across an armature gap, a coil rotatively suspended in such gap, a torsional suspension for suspending such coil, and means for nullifying the torque of such suspension when the coil is rotated in either direction from a neutral position where the suspension has no torque comprising a miniature permanent magnet connected to said coil adjacent such suspension Abut displaced from the immediate vicinity of and lying in the leakage eld of the stationary permanent magnet means and polarized in a direction to oppose such leakage field when the coil is in a neutral position, a pair of magnetic members lying parallel to and on opposite sides of said miniature permanent magnet in leakage flux shunting rela-tion thereto and adjustable toward and away therefrom for adjusting the influence of the leakage eld on said miniature magnet, and another magnetic member lying in said leakage eld between the stationary magnet means and miniature permanent magnet and adjustable so as to modify the relative distribution of leakage iield flux between said pair of magnetic members.

2. A galvanometer comprising stationary permanent magnet means for producing a field through an armature gap, an armature coil rotatively suspended in said gap, a torsional suspension for said coil, and means for substantially nullifying the torque of such suspension when the coil is turned in either direction from a neutral position where the suspension torque is zero, comprising a miniature permanent magnet fastened to'said coil and positioned closely adjacent said suspension within theleakage field of the stationary permanent magnet means and polarized in a direction to oppose such leakage field when the coil is in a neutralposition and means for adjusting the influence of said miniature permanent magnet comprising a pair of magnetic members positioned on opposite sides of the polarized axis of said miniature permanent magnet in leakage flux shunting relation thereto so as to diminish the leakage flux in the immediate vicinity of said miniature permanent magnet and strengthen it on either side of said miniature permanent magnet, and means for individually adjusting each of said pair of magnetic members toward and away from said permanent magnet.

3. A galvanometer of the suspension type comprising an outer housing part and an inner part which lits within the housing part in removable telescoping relation, said outer part including stationary permanent magnet means for producing a eld through the inner part, said inner part including a coil and a suspension therefor for torsionally suspending said coil within said field, means for adjusting said suspension for determining the rotary neutral position of said coil in said field when there is zero suspension torque, means carried by said inner part for substantially nullifying the torque of said suspension within the deflecting range of the coil in either direction from neutral position comprising a miniature permanent magnet fastened to said coil closely adjacent the suspension in the leakage eld of said stationary permanent magnet means and polarized to oppose such leakage eld when the coil is in a neutral position, a pair of magnetic means carried by said inner part on either side of said miniature` permanent magnet for shunting leakage flux from the immediate vicinity of the miniature permanent magnet, said means being individually adjustable toward and away from the miniature permanent magnet, and magnetic means vsupported on the outer housing part in series relation in the leakage flux iield with said pair ofmagnetic members, said part being adjustable about the axis of suspension of said coil for varying the relative distribution of the leakage flux between said pair of magnetic members, all of said adjustments being accessible for adjustment purposes with the inner and outer parts in telescoping assembled relation.

LORIN OBRYAN. 

